1. Field of the Invention
The present invention relates to an alkaline battery having desirable load characteristics and a method for producing the same.
2. Description of the Related Art
An alkaline battery containing zinc as a negative active material is used as a power source of various kinds of electronic equipment, and is required to have various characteristics depending upon its use. Particularly, in a digital camera that has been widely spread in recent years, in order to maximize the number of photographs, it is necessary to increase the capacity of a battery and further enhance load characteristics such as large current discharging characteristics. Design of a battery that can satisfy the requirements has been studied.
In order to increase the capacity of a battery, it is necessary to increase the amount of an active material. However, if the active material is not used effectively for discharging, an increase in the capacity of a battery cannot be achieved. Therefore, the above object cannot be achieved merely by increasing the amount of the active material. The discharge capacity is dependent on the utilization factor of the active material, so that it is important to ensure satisfactory conductivity of the active material and to uniformly fill the battery with the active material. Also, it is necessary that a positive electrode, a negative electrode, and an electrolytic solution are designed so as to allow a discharging reaction to proceed smoothly.
Furthermore, in order to enhance load characteristics, it is necessary to increase a reaction area of the active material and to enhance conductivity. Along with an increase in the reaction area of the active material, gas is likely to be generated due to the reaction with an electrolytic solution. Therefore, zinc, which is in a negative electrode and is a negative active material, generally is formed into an alloy with an additive element capable of suppressing the generation of gas.
However, due to the increase in the battery's content of the additive element, conductivity is likely to be decreased. Therefore, it is difficult to satisfy both the suppression of the generation of gas and load characteristics. Furthermore, a zinc compound (in particular, zinc oxide) generally is contained in an electrolytic solution so as to suppress self-discharging, which may decrease load characteristics.
Furthermore, even if a battery with desirable load characteristics can be designed, another problem described below occurs, so that there still remain problems to be solved in order to obtain a practical battery. More specifically, the storage property at high temperature may be degraded, a battery may be short-circuited erroneously or by the malfunction of electronic equipment. Accordingly, when an excess current flows through a battery, the temperature of the battery increases due to the heat generated therein, which may cause leakage of an electrolytic solution and a rupture of the battery. In particular, as a capacity of a battery is increased and a battery is designed for a higher load, the reactivity of an electrode is increased, and the amount of heat generation is increased.